EXPERIMENTAL STUDY ON SPATIAL DROPLET SIZE DISTRIBUTION OF DIESEL SPRAY INJECTED BY HOLE-TYPE NOZZLE USING IMAGING-BASED TECHNIQUE — EFFECT OF INJECTION PRESSURE

The spatial droplet size distribution directly determines the spatial uniformity of fuel−air mixture, and then further influences the combustion and emission performance. An imaging-based technique is employed in this study to capture spray droplets at different positions (eight positions along the spray axis and six positions on the spray periphery) under three injection pressures (60, 100, and 140 MPa). The ambient pressure is maintained at 2 MPa. Droplet characteristic parameters such as droplet velocity, droplet diameter, and minimum distance are analyzed. The experimental results indicate that regardless of injection pressure, the size distribution curve along the spray axis changes from unimodal to bimodal, and then from bimodal to unimodal. Meanwhile, the Sauter mean diameter (SMD) along the spray axis firstly increases, and then stabilizes for a certain range before finally decreases. The SMD on the spray axis is larger than that on the spray periphery and no definite relationship exists between the droplet diameters on the spray periphery. Regardless of the measurement position, a higher injection pressure yields smaller spray droplets. The mean minimum distance between droplets increases along the spray axis, and the higher the injection pressure, the smaller is the mean minimum distance. However, at a measurement position near nozzle, a higher injection pressure contributes to a larger minimum distance. Relevant conclusions regarding the spatial distribution characteristics of the spray droplet size and minimum distance can be used to validate and improve the existing spray atomization model and droplet size distribution function.